There are 3 qualities for any being or existence, named as : Sattva (illumination), Rajas (passion), Tamas (ignorance).
Gita discusses them in great detail. According to it, the quality of Rajas is the reason for bondage or attaching a jiva to the physical plane, which resides in between the heaven (due to good deeds caused by Sattva) and the hell (due to sins caused by Tamas). Rajas has to be pacified for the liberation (viz. Moksha).
These leaves us with Sattva and Tamas. It indirectly implies that, the prominence of these 2 'may' not obstruct the liberation. Sattva being illuminating, would bring a consciousness to higher regions of life followed by Moksha.
Tamas on the other hand is related to ignorance and dumbness, which 'might' cause fall of a consciousness.
According to many verses, the sinfulness has no relation with the liberation. For example, verse BG 9.32 says that, sinful beings like Stri (Women), Vaishya (business class), Shudra (service class) also get liberation. Also refer BG 9.30.
[There is a local temple in my hometown. Its Mahant (prime priest) suggested that, opt for Stri Bhakti when possible, it's liked by the lord a lot.]
There are many bAwA-s (e.g. नागा साधु), who eat stale food, smoke and remain lazy in their life. Which are all notebook TAmasik qualities.
Now if Tamas brings to hellish regions, then why should such people be called Yogi-s or spirituals, isn't it?
As opposite argument, it's also said in BG 16.20, that those people who don't resolve their anger, lust, greed -- keep falling into lower & lower hells. But the further question is, how far can one fall? There has to be a limit of falling. One must be liberating after the last fall.
[Famous English saying related to tamas: "Ignorance is Bliss!"]
- Does the quality of tamas cause the liberation?
- If yes, then is the liberation via tamas quicker/slower than the sattva?
Clarification: For the liberation, one has to become gunAtita (beyond  qualities). But this question is not about it. Like how prominent Rajas obstructs the liberation, I want to know how the prominence of Tamas affects the liberation.